poimen/tasks/T5.1-taskid-at-spawn.md

T5.1 — TaskId at spawn

Field	Value
Phase	P5 — Grading
Size	S — under 1 day
Status	Not started
Flags	—
Spec	inlined below
Blocks	T5.5 onward. Cannot be retrofitted

Goal

Every run carries a TaskId from spawn. Required, no default, no derivation from RunId.

Facts (inlined — no spec read needed)

• TaskId is the comparison-group key: a content hash of the task input before any workflow touches it.
• Hashing the prompt does not work — the workflow changes the prompt by construction, which is the entire point of a variant.
• TaskId cannot be backfilled. A run recorded without one is permanently ungroupable and useless to the learning loop. Hence: required at spawn, no Default, no From<RunId> (T0.1).
• Land this during P1, even though nothing consumes it until P5. It is a small task deep in P5 and it is the one item on the critical path that a later phase cannot repair.
• What defines TaskId for a given user is open — ticket id, input fixture, or a hash of the pre-workflow goal. The framework provides the type and a default hasher and lets it be overridden. Settle it before any run is recorded.

Steps

1. Add task: TaskId as a required positional field of the spawn parameters. Not Option, not a builder method that can be omitted.
2. Provide a default hasher over the pre-workflow task input, and a hook to override it. Document that the choice is permanent for existing data.
3. Record TaskId on the run's spawn event so it lands in the log, not only in materialized state.
4. Expose it on EpisodeView for the grading path.
5. Add the trybuild compile-fail case: a spawn call omitting TaskId.

Acceptance

• Spawning without a TaskId fails to compile.

Verify

Harness: trybuild, plus a full run to prove the id reaches storage.

Integration test — tests/it_taskid_required.rs:

1. trybuild compile-fail: a spawn call omitting TaskId. Assert the expected stderr names the missing field, not merely "does not compile".
2. Run a real run; read the log (not materialized state) and assert the spawn event carries the TaskId.
3. Assert EpisodeView exposes it, so the grading path can group on it.
4. Determinism: hash the same task input twice, in two processes; assert equal TaskId.
5. Independence: assert two runs of the same task input share a TaskId, and that two different inputs do not. Both directions.
6. Assert the TaskId is not derived from the prompt: change the workflow version (which changes the prompt) and assert the TaskId is unchanged for the same input.
7. trybuild: TaskId::default() and TaskId::from(run_id) both fail.

Command: cargo test -p kernel taskid && cargo test -p kernel --test compile_fail

False pass:

• Step 2 read from materialized state. If the id lives only in state it cannot be re-derived after a cold fold, and it cannot be backfilled — read the log.
• Step 6 omitted: hashing the prompt passes steps 1–5 completely and makes every variant its own group, which is the exact failure that renders the learning loop inert.
• A builder with a runtime expect("task_id required"). It passes a test that checks for a panic and still allows runs to be recorded without one in any code path the test did not cover.

Traps

• A builder with .task_id(...) optional and a runtime check. Runs recorded before someone notices are unrecoverable.
• Deriving it from the prompt or from RunId. Both compile; both make every run its own group of one.

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Background (not required to do this task): rust-agentic-sys.md §3, §11.5, §18 · rust-agentic-task.md